1. Field of the Invention
The present invention relates to a tiltable or tilt-in-space wheelchair.
2. Description of Related Prior Art
Various forms of tilt-in-space wheelchairs are known in which a seat frame is tiltable relative to a wheeled base frame for various known benefits including providing weight shift and pressure redistribution, repositioning for comfort and pain relief, and providing postural stability.
Some examples of tilt in space wheelchairs can be found in U.S. Pat. Nos. 6,206,393 and 6,126,186 by Mascari et al; U.S. Pat. No. 7,007,965 by Bernatsky et al; U.S. Pat. No. 7,185,910 by Beauchesne et al; and U.S. Pat. No. 7,090,240 by Papac. Other prior art relating generally to tilting seats can be found in U.S. Pat. No. 2,195,428 by Searing; U.S. Pat. No. 4,515,337 by Torras; U.S. Pat. No. 7,850,238 by Erb et al; and U.S. Pat. No. 4,192,549 by Petersen.
The state of the art in the tilt chair industry is to provide wheelchair seating systems on bases that use arcuate tracks that have a substantially constant-radius arc with a focal point adapted to be substantially coincident with the center of gravity of the user. This alignment creates an easy rotation of the supported weight as the CG of the system is not being actively lifted or lowered in the act of tilt.
A potential issue with this approach is the need for set-up of the user and the seating system center of gravity to be closely aligned. Lack of a reliable feedback method to actively manage the set-up and mistakes in set-up can lead to misalignment where-by the seating system is not always stable in the supporting track system. The seating system and user weight can act like an “inverted pendulum” and the supported weight creates a force that actively rotates the system in the supporting tracks, with the potential of the system slamming in either a forward or upright position. In practice this can create a rather unsafe event for the user and for the care-giver.